1. Field of the Invention
The present invention relates to a broadband wireless access system. More particularly, the present invention relates to an apparatus and a method for supporting multicast communication in a broadband wireless access system.
2. Description of the Related Art
In general, wireless communication systems have been developed mainly for voice service. Based on advances in technology, wireless communication systems now also provide data service and various multimedia services as well as the voice service. However, the voice-oriented communication system, which uses a relatively narrow transmission bandwidth and imposes expensive fees, has not satisfied increasing service demands of users. Moreover, advances in the communication industry and the increasing demand of users for Internet services create the necessity for a communication system that efficiently provides such advanced services. In this respect, a broadband wireless access system is introduced to efficiently provide Internet services with enough bandwidth to meet the increasing demand.
The broadband wireless access system supports not only the voice service but also various low- and high-speed data services and multimedia application services such as high quality video. The broadband wireless access system can access a Public Switched Telephone Network (PSTN), a Public Switched Data Network (PSDN), an Internet network, an International Mobile Telecommunications-2000 (IMT-2000) network, and an Asynchronous Transfer Mode (ATM) network based on wireless media using broadband frequencies such as 2 GHz, 5 GHz, 26 GHz, and 60 GHz in the mobile or stationary environment, and support a channel transfer rate of over 2 Mbps. Based on the mobility of a terminal (e.g., stationary or mobile), the communication environment (e.g., indoor or outdoor), and the channel transfer rate, the broadband wireless access system can be classified into a broadband wireless local loop, a broadband mobile access network, and a high-rate wireless Local Area Network (LAN).
The wireless access scheme of the broadband wireless access system is standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard group which is a standardization organization. An IEEE 802.16 standard system can transfer much data within a short time over the wide bandwidth and efficiently utilize the channel by allowing all users to share the channel (or resources), compared to conventional wireless technologies for the voice service. Also, because Quality of Service (QoS) is guaranteed, each user can enjoy services of different qualities according to characteristics of the service.
The IEEE 802.16 standard defines a Multicast and Broadcast Service (MBS) specification for multicasting and broadcasting data to a plurality of Mobile Stations (MSs). The MBS specification can distinguish common or overlapping multicast and broadcast service areas using different Connection IDentifiers (CIDs) or different Security Associations (SAs). Herein, an MBS zone is used to indicate a region where broadcast and multicast service flows are valid through the CID and the SA, and a Base Station (BS) broadcasts MBS zone information using a Downlink Channel Descriptor (DCD) message.
However, a conventional Multicast CID (hereafter, referred to as an MCID) allocation method for the multicast channel has the following shortcomings. In the near future, it is expected that the bandwidth of many broadcasting technologies such as cable TV or Digital Multimedia Broadcasting (DMB) will increase such that the user can select from hundreds of video, audio and data channels. In this respect, the system can provide the service by grouping the hundreds of channels on a regional basis considering the national scale. However, only 94 MCIDs are allowed according to the specification. As a result, it is impossible to allocate unique MCIDs to the hundreds of channels. Besides, the IEEE 802.16m standard defines a 12-bit STation IDentifier (STID) for identifying the MS, only for the unicast to the MS.
To address those shortcomings, it is necessary to newly define an ID for identifying the MS to support the multicast and an ID for distinguishing the service.